Speed-control system



Dec. 4,192& 1,694,322'

J. l. HULL SPEED CONTROL SYSTEM Driginal Filed Feb. 17, 192*! Inventor:John I. HUN

His Attofnev Patented Dec. 4, 1928.

UNITED STATES PATENT OFF-ICE.

JOHN I. HUIZLKOF 'SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRICCOMPANY, A CORPORATION'OF NEW YORK.

SPEED CDNTROL SYSTEM.

Original applicationfiledlebrmary 17. 1927, Serial No. 169,074. Dividedand this application filed Iovember 23, 1927.

My invent-ionrelatesto speed control systems for induction motors andhasfor itsobject the provision of ail-improved arrangemenlnfor controllingtheexcitation of a commutator machine whichis concatenated with aninduction motor for the purpose of-controlling itsspeed.

Thetheory of thecontrol'of the speed of induction motors by means of)olyphase l0 commutator regulating-machines oi the wellknown Scherbiu-stype in which the rotor is provided with a commutated winding andthcrstator with a neutralizing winding and an independent excitingwinding has been pointed out in my United States Patent 1,306,594,assigned to the same assignee as the presentinvention. It is showntherein that this ideal regulation requires the injection intotheindependent exciting winding of the regulating machine-of onecomponent of voltage independent of slip frequency for the purposeofbalancing the resistance drop in said exciting winding and asecond-component of voltage varyingin ap r roximate pro- 26 portion tothe slip frequency or the purpose of balancing the inductive drop.Thepresent application, which is a'division of my application Serial No.169,074 filed 'February 17, 1927, relates to improvements in the nomeans for accomplishing such regulation in accordance with theseconditions.

In carrying my invention into effect I prefer to makeuse ofa commutatorexciting machine which is driven at a speed directly proportional to theslip frequency, the speed being zero at zero slip, for supplyingtheinductive drop excitation. This machincalways operates at itssynchronous speed or approximately its synchronous speed and 40consequentlythe flowof current in its armature winding isalways-directcurrent or an alternating current of very low freuencywhich gives the advantage of a=negligi le reactance drop in thearmature. The rotor and stator windings then function as the primary andsecondary windings of a transformer, the transformation ratio of whichis directly proportional to the speed of rotation. This supplies thevoltage necessary for supplying the inductive drop in the excitingcircuit of the main regulating machine and other means are provided forsupplying the additional ex- Serial No. 235,368

'citationcomponent required for the correct regulation of the speed ofthe induction motor.

Referring to the drawing, 10 represents the main induction motorsupplied from source 11. The secondary circuit 28 of the main motor isconnect-ed to the commutator brushes of the regulating machine 12 whichmachine is driven by the motor 14 floating on line 11. The field 13 ofthe regulating machine has one end connected to the frequency changer 16which is driven by the main motor. The frequency converter which might,if desired, be supplied by an auxiliary synchronous enerator is shownsupplied from line 11 through suitable regulating resistances and atransformer. The primary of this transformer is shown at 40. 41comprises a secondary winding of this transformer which is connected tothe frequency converter 16 through adjustable resistances 42 to supplythe excitation neccssary for overcoming the resistance drop in thecircuit of the field winding13. A further secondary transformer winding43 arranged in quadrature relation with winding 41, together withadjustable resistances it may be provided if desired to supply a voltageto the frequency converter for adjusting the power factor of motor 10.Machine 41-5 has a distributed pol yphase stator winding46, similar tothat of an induction motor, connected in the field circuit 13 and anarmature similar to that of a direct currentmachinc-connected throughpolyphase brushes and a calibrating resistance 47 to the commutator endof the frequencyconverter 16. This machine 45 is driven by the motor 27from the secondary circuit 28 of the main motor. Machines 27 and .5willhavethe same number of poles and'accordingly machine 4:5 is drivenat a synchronous speed corresponding to the slip frequency of the mainmotor 10. The frequency obtained at the commutator end ofthe frequencyconverter 16 is exactly equal to the slip frequency of 10. If 27 is asynchronous motor, machine 45 will run at exactly its own synchronousspeed and at approximately synchronous speed if 27 is an inductionmotor. In the first case mentioned there is no voltage induced in therotor winding of 4:5 and in the second case but a very slight voltage,so that the current rip "i'cqncncy i said induction inoioit.

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